PPL Therapeutics is developing transgenic alpha-1-antitrypsin for the treatment of cystic fibrosis lung disease and other conditions in which connective tissue is broken down irreversibly. AAT is a plasma protein that inhibits elastase, a key player in the inflammatory response that, unchecked, will lead to excessive tissue destruction. PPL has taken transgenic alpha-1-antitrypsin through phase II clinical trials in the cystic fibrosis lung, delivering it in aerosol form to assess its safety and efficacy [315887]. Although early results are not statistically relevant with respect to clinical benefit, they do show some promise, especially given the low numbers of patients studied and the complex phenotypes and severities associated with cystic fibrosis.